Heart valve replacement is required when a patient's heart valve becomes diseased or damaged. Surgically implanted heart valve prostheses have extended the life expectancy of many patients with defective heart valves. Such prostheses can be either mechanical or biological (tissue valves), stented or stentless, and may be implanted into an aortic, mitral, tricuspid, or pulmonary position.
During this surgical procedure, the heart is typically stopped and the patient attached to a heart/lung bypass machine that pumps and oxygenates the patient's blood. The longer a patient is required to rely on the artificial heart/lung bypass machine to maintain vital functions, the greater the stress on the patient. There is consequently a need to simplify the surgical implantation of a heart valve prosthesis into the implantation annulus in order to minimize both the length of surgery and the amount of time spent on heart/lung bypass.
Stented heart valves made from flexible material or from materials that exhibit shape memory characteristics promise less complicated and faster valve implantation procedures. The stents supporting the heart valves are generally cylindrical in shape and are structured to be crimped so as to reduce their size for delivery to a target site. The crimped stent and attached heart valve may be delivered to the target site with any suitable means, such as a catheter or the like. Once positioned in the desired location, the stent may be re-expanded to secure the heart valve in place by exerting radial forces against the internal walls of the implantation annulus. The stents may be either self-expanding or non self-expanding. Self-expanding stents may be formed from any suitable shape memory material, such as Nitinol. Non self-expanding stents are typically expanded via an inflation means or mechanical expansion means. Stented heart valves are sometimes referred to as suture-less valves since they may be implanted and secured into the annulus without the use of sutures.
As appreciated by those skilled in the art, it is desirable to crimp the stent in a substantially uniform manner to minimize the variation in pressures applied to the stent. Such pressure variations may lead to deformation of the stent, which may reduce the ability of the stent to securely maintain the heart valve at the target location. Thus, if a stent is crimped in a non-uniform manner, it is typically either re-crimped or thrown away. Re-crimping of stents is not desirable because the repeated application of force on the stent may cause fatigue or weakening of the stent structure. Disposing of poorly crimped stents is also not desirable due to the increased costs associated with the waste. This is especially true with stented heart valves because the stent and the heart valve are attached together and must be disposed of as a single unit.
Therefore, what is needed is an improved device and method for radially crimping a stent from a first diameter to a reduced second diameter. What is further needed is an improved device and method that provides substantially uniform crimping, minimizes unnecessary waste, and allows a crimped stent to be easily loaded into a delivery device.